The curtain air bags are mounted in the front and rear window pillars, and the roof edge along both sides.
When the air bag crash sensors detect a side impact of greater than moderate force, the curtain air bag inflates quickly and helps to reduce injury mainly to the rear outboard passenger's head caused by directly hitting interior parts such as a door or window. For more details about air bag deployment, refer to "SRS Air Bag Deployment Criteria".
In a side impact:
Greater than moderate impact to one side of the vehicle will cause the curtain air bag on that side only to inflate.

(With Front Passenger Occupant Classification System) In a roll-over:
In response to a vehicle roll-over, both curtain air bags inflate.

Warning Light/Beep
A system malfunction or operation conditions are indicated by a warning.Refer to Warning/Indicator Lights. Refer to Warning Sound is Activated.
Side Air Bags
SRS Air Bag Deployment CriteriaMazda 6 Owners Manual: Tire Maintenance
Improper or inadequate vehicle maintenance can cause tires to wear abnormally.
Here are some important maintenance points:
Tire Inflation Pressure
Inspect all tire pressure monthly (including the spare) when the tires are cold.
Maintain recommended pressures for the best ride, top handling, an ...
Mazda 6 Owners Manual: Dual proportioning valve replacement (without abs)
1. Remove in the order indicated in the table.
2. Install in the reverse order of removal.
Dual Proportioning Valve Installation Note
Install the dual proportioning valve so that the R mark faces the left side
of the vehicle.
...